1. Field of the Invention
The present invention relates to phase-locked loops (PLL), and more particularly, to PLLs utilized in optical disc drives.
2. Description of the Prior Art
Phase-locked loops (PLLs) include analog PLLs, digital PLLs, and hybrid PLLs, where hybrid PLLs have both digital components and analog components for locking on a reference signal to generate an oscillating clock signal.
In addition to comprising a PLL for locking on an RF signal read from a pickup head, an optical disc drive further comprises a PLL for locking on a wobble signal read from the pickup head, in order to support reading and writing operations of the optical disc drive. Furthermore, in order to maintain output of a steady clock signal while switching between a reading mode and a writing mode of the optical disc drive, an analog circuit design can be utilized to combine the PLL for locking on the RF signal and the PLL for locking on the wobble signal, so that the two PLLs share a common portion of components and thereby maintain a steady clock signal output.
However, the analog circuit design of implementing a combined circuit of two PLLs mentioned above does not have the advantages of digital circuitries, such as high adjustability, and greater tolerance to inaccuracy caused by manufacturing process variations.